The power drive system of a subsea boosting application consists of a Variable Speed Drive supplying power to the subsea booster pump through an umbilical. Transformers may be used to elevate the transmission voltage for longer step outs (typically >15km).

The induction motor for OneSubsea Processing applications have for more than 20 years had a voltage rating at max 6.6kV based on standard motor classing. It was designed for continuous operation with a single earth fault in compliance with IEC voltage class 6/10(12) kV (IEC 60502). As a result of our comprehensive and successful track record, operation with earth fault has been removed as a firm requirement for some applications, allowing the rated operating voltage to be increased.

Elevating the rated motor voltage and hence the transmission voltage, enables subsea boosting applications with longer step out, eliminating the need for step-up/-down transformers. In 2016 OneSubsea launched and successfully executed a fast track development- and qualification program including design activities, analyses, test and manufacturing of a prototype 10.5kV High Voltage Motor unit.

The qualification of an induction motor with increased voltage rating was since then been the enabler for the award of two major boosting system projects.

The possibility of a simplified layout can now contribute to a significant reduction in installation cost, complexity and risk associated with the deployment of systems with subsea transformers. However a holistic system approach needs to be considered to determine the best cost and value engineered solution.